In principal, amphoteric ion exchangers are distinguished in that they comprise acidic and basic functional groups next to one another. Processes for production thereof are described in Helfferich Tonenaustauscher [ion exchangers], volume 1 page 52, Verlag Chemie, Weinheim or in Bolto, Pawlowski, Wastewater Treatment, Spon, London, 1986, page 5.
Stach, Angewandte Chemie, 63, 263, 1951 describes amphoteric ion exchangers which comprise strongly basic and strongly acidic groups next to one another. These amphoteric ion exchangers are produced by copolymerization of styrene, vinyl chloride and a crosslinker such as, for example, divinylbenzene, followed by quaternization and sulfonation.
DE-A 10353534 describes amphoteric ion exchangers which comprise not only weakly acidic but also weakly basic groups next to one another. As weakly basic groups, mention is made of primary amino groups, as weakly acidic groups, mention is made of acrylic acid and alkyl(C1-C4) acrylic acid groups such as, for example, methacrylic acid.
All of said amphoteric ion exchangers share the fact that they are not very suitable for complex separation processes, in particular for chromatographic separation processes. Their slow kinetics, low selectivity and separation efficiency are generally insufficient therefor.
It was therefore the object of the present invention to develop novel amphoteric ion exchangers which exhibit good separation efficiency, sufficiently rapid kinetics and high selectivity and also stability, in particular in separations of organic mono-, di- or polycarboxylic acids from aqueous solutions, in particular fermentation broths.